Sir Richard Branson surprised good friend and tennis ace Marion Bartoli by "proposing" to her with a ring she had previously lost on Necker Island.

The former Wimbledon champion had misplaced the jewel one year ago when she was playing tennis on his private island, and had thought she had lost it forever.

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"My wife has given me permission to have a second wife," joked Richard, standing in front of a group of friends. "I know that she's already got a boyfriend but I just want to propose to her. You have to come forward, Marion, you."

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"Oh my God, what is it?" said a shocked Marion.

"I'm proposing," said Richard, to which Marion replied, "What are you proposing?"

"What do you think? Will she accept? Will you accept?" he added.

"Of course I'm accepting but what am I accepting," laughed Marion, after which Richard pulled out her gold ring. "Ah you found my ring, you found my ring!"

Marion, 29, had been given the piece of jewellery as a present after she won Wimbledon in 2013.

"I was so excited I smashed the ball and the ring flew over and dropped in the sand," she explained to the group. "And we started to go all over the sand but we couldn't find it and you know everyone told me, Richard is going to try and find it forever until he finds it. And I can't believe he found it a year later."

The tennis star and the Virgin Group magnate, 64, have been taking part in the Virgin STRIVE challenge – an ultra-endurance event which involves a core team travelling from London to the summit of the Matterhorn in Switzerland, entirely under human power.

The Virgin STRIVE challenge raises money for Big Change, a charity founded by six friends including Richard's children Sam Branson and Holly Branson, and their good friend Princess Beatrice. The charity works with young people in the UK and helps them develop crucial life skills including communication, resilience and teamwork.